1. Field of the Invention
The present invention is directed to image sensors and, more particularly, to systems for reading out the contents of pixels in image sensors.
2. Discussion of Related Art
Image sensors are used to generate images based upon the outputs of a large number of light-sensitive pixels arranged in an array. Each pixel in such an array generates an output signal that is proportional to an amount of light that is incident on that pixel during a so-called xe2x80x9cintegration period.xe2x80x9d All of the pixels in an array generally are permitted to xe2x80x9cintegratexe2x80x9d for a predetermined amount of time during an integration period and the contents of the pixels are individually xe2x80x9cread outxe2x80x9d during a so-called xe2x80x9cread out period.xe2x80x9d
Pixels may be arranged in a linear array of xe2x80x9cnxe2x80x9d pixels (a linear sensor). Such a linear (one-dimensional) array of pixels may be moved in a direction perpendicular to the direction in which the array is oriented to a number of equi-spaced positions, integrating and reading out the contents of the pixels at each position, in order to measure the light incident on a two-dimensional area.
In a complementary metal oxide semiconductor (CMOS) linear sensor, a single array readout line generally is used to read out the contents of the pixels in the sensor""s linear array, and outputs of each of the pixels in the array are sequentially provided to the array readout line (e.g., via switches). A certain period of time is required to allow the signal on the array readout line to settle before using external circuitry to measure the signal on the line. The speed at which the contents of pixels may be read out of the array therefore is limited by the settling time of the readout line. This settling time is determined primarily by the capacitance of the array readout line.
The switches that selectively provide the contents of the pixels to the array readout line generally are implemented using metal oxide semiconductor (MOS) transistors. Each of these MOS transistors has a gate-to-source or gate-to-drain capacitance associated with it that, when connected to the array readout line, incrementally increases the readout line""s overall capacitance. The capacitance added by each of these switches therefore limits the rate at which the outputs of the pixels can be selectively provided to the array readout line.
Similarly, because each of the switches is connected to the array readout line via a circuit trace having a particular length, each such circuit trace incrementally increases the overall capacitance of the array readout line. The capacitance added by each of these circuit traces to the array readout line also limits the rate at which the outputs of the pixels may be selectively provided to the array readout line.
What is needed, therefore, is an improved pixel readout scheme for image sensors.
According to one aspect of the present invention, an image sensor includes a linear pixel array and array readout lines. The linear pixel array includes a group of pixels arranged in a row. Each array readout line is selectively coupled to an output of at least one pixel included in group of pixels.
According to another aspect of the invention, an image sensor includes a linear pixel array and an array readout line. The linear pixel array includes a first group of pixels, sensitive to a first color of light, arranged in a first row, and a second group of pixels, sensitive to a second color of light, arranged in a second row. The array readout line is selectively coupled to outputs of pixels included in the first group of pixels and outputs of pixels included in the second group of pixels.
According to another aspect, an image sensor includes array readout lines and a pixel. An output of the pixel is selectively coupled to each of the array readout lines such that the contents of the pixel may be provided to any one of the array readout lines without being provided to any other of the array readout lines.
According to yet another aspect, an image sensor includes a linear pixel array and array readout lines. The linear pixel array includes a group of pixels, sensitive to a particular color of light, arranged in a row. Each array readout line is selectively coupled to an output of at least one pixel included in the first group of pixels.